1. Field of the Invention
The invention relates to an image display apparatus using electron-emitting devices.
2. Related Background Art
Flat panel type image display apparatuses have been vigorously being studied and developed as display apparatuses of images, characters, and the like. A large panel display screen size and high definition are demanded for the flat panel type-image display apparatuses.
In a PDP, an LCD, and an SED (surface conduction type electron-emitting device display) as flat panel type image display apparatuses, flat panel glass is used and a thickness of image display apparatus lies within a range from a few cm to tens of cm and is thinner than general CRTs. Although those display apparatuses are of the flat panel type, actually they have a warp of about a few mm or less which is caused due to a manufacturing processor the like. There is a case where a color variation and a luminance variation are caused by such a warp.
The image display apparatus in which such a warp occurred has been disclosed in for example, JP-A-2003-109528 and is shown in FIG. 13.
FIG. 13 is a schematic cross sectional view of a panel main body using electron-emitting devices. A frame-shaped supporting spacer 40 is interposed between a face plate 30 and a rear plate 20 in which a number of electron-emitting devices 10 are arranged in a matrix shape on one surface side. A space formed by those plates 20 and 30 and the spacer 40 is held in a vacuum state. A collector electrode made of an ITO film is formed on the surface of the face plate 30 which faces the rear plate 20. Each electron-emitting device 10 is arranged every sub-pixel 32 consisting of one phosphor cell (phosphor layer). Each sub-pixel 32 is excited by an electron beam which is irradiated from the electron-emitting device 10 and emits light to a color region of one of the three primary colors of R, G, and B. As shown in the diagram, the face plate 30 has a curved shape which is convex to an outer surface side.
As for the sub-pixels 32 provided for the face plate 30, a pitch between the sub-pixels 32 is set so that sizes of projection images onto the one surface of the rear plate 20 in the sub-pixels 32 are made coincident. Therefore, the projection image of the sub-pixel 32 is almost equal to the surface shape of the electron-emitting device 10 and is overlapped to the electron-emitting device 10. Consequently, it is possible to prevent the electron emitted from the adjacent electron-emitting device 10 from reaching, a blur of an image can be prevented, and color reproducibility can be improved.
FIG. 1 is a schematic cross sectional view schematically showing a structure of a panel which is used in the flat panel type image display apparatus. Reference numeral 101 denotes a rear plate; 102 a face plate; 103 a frame; and 104 a panel obtained by sealing and bonding the rear plate 101, face plate 102, and frame 103 by a panel sealing step. The inside of the panel 104 is held in a vacuum state. Reference numeral 105 denotes an electron source pattern formed on the surface of the rear plate 101 which faces the face plate 102. The electron source pattern 105 is formed by a plurality of electron-emitting devices. Reference numeral 106 denotes a phosphor pattern formed on the surface of the face plate 102 which faces the rear plate 101. The phosphor pattern 106 is formed by a plurality of phosphor (light-emitting members) and each phosphor corresponds to each electron-emitting device.
There is a case where a temperature difference or the like occurs between the rear plate 101 and the face plate 102 in a thermal process in the panel sealing step. Thus, there is a case where the rear plate 101 and the face plate 102 which were almost flat surfaces before the panel sealing step are warped after that, so that the panel 104 is warped as illustrated in FIG. 1.
There is also a case where the fear plate 101 or the face plate 102 is sealed and bonded in the panel sealing step by using a hot plate while being pressed, or the like. In the hot plate, there is a case where a slight warp is caused by a thermal distortion and the hot plate becomes a non-flat surface after the sealing step is repetitively executed.
In the panel in which such a temperature difference occurs or the panel which was sealed and bonded by the warped hot plate, a warp occurs and the panel becomes the non-flat surface. Such a warp becomes remarkable with an increase in panel size.
In the flat panel type display apparatus, there is a case where a spacer is interposed between the face plate and the rear plate so that a space between the rear plate 101 and the face plate 102 is not broken by the atmospheric pressure. In the case of such a construction, since the rear plate 101 and the face plate 102 are pressed to the spacer by the atmospheric pressure, a macroscopic radius of curvature of the whole rear plate 101 and that of the whole face plate 102 almost coincide.
It is now presumed the panel 104 in which the electron source pattern 105 and the phosphor pattern 106 are formed at the same size on the rear plate 101 and the face plate 102 in the almost flat surface state, respectively, and the panel 104 is sealed and bonded so that a center position of the rear plate 101 and that of the face plate 102 coincide. An electron beam emitted from the electron-emitting device is irradiated in the direction of a normal line of the rear plate in the electron-emitting device. Therefore, if the panel is warped by the foregoing reasons, a difference of δ/2 occurs in each of both ends as shown in FIG. 1.
In other words, a position of a center of gravity of phosphor which should inherently exist does not exist in the direction of a normal line of a position of a center of gravity of a certain electron-emitting device or apposition of a center of gravity of the emitted electron beam, so that a deviation occurs in an irradiating position of the electron beam to the face plate. Such a situation is illustrated in FIG. 14.
When the electron beam is deflected by a deflecting voltage or the like, an ideal position of the center of gravity of phosphor is set in consideration of its deflection amount and a similar idea is used.
Although such a positional deviation due to the warp is small at the center of a display screen, it increases as a position approaches an outer position of the display screen. When the positional deviation is small, there is no problem as picture quality.
However, as the positional deviation amount increases, the electron beam is deviated from phosphor to be inherently irradiated by the electron beam, so that luminance decreases. Further, when the positional deviation increases, phosphor adjacent to phosphor to be inherently irradiated by the electron beam is irradiated, so that a color drift occurs in the case of a color television. Such a color drift becomes a typical problem with an increase in size of display screen.
The decrease in the luminance can be suppressed to a certain extent by increasing a size of phosphor to a value larger than abeam size. However, in the case of a high-definition display apparatus, the positional deviation becomes a remarkable problem.
As mentioned above, the positional deviation which is caused by the warp of the airtight container (panel) will become an important problem in association with the realization of a large screen size and high definition of the image display apparatus in the future.